Understanding Weak Intermolecular Forces in Molecular Crystals

The bulk macroscopic properties (such as melting point and solubility) of solid-state materials are governed by weak intermolecular forces that originate from atomic-scale interactions. These forces range greatly in strength and specificity from the biologically critical hydrogen bond to the ubiquitous London dispersion force. Terahertz spectroscopy is able to directly probe intermolecular forces through the low-frequency vibrations exhibited by molecular crystals. Combining terahertz spectroscopy with solid-state density functional theory calculations (including corrections for weak London forces) enables a detailed understanding of intermolecular forces to be obtained in a variety of solids such as pharmaceutical polymorphs and crystalline solvates.